The present invention relates to a thermal drop detector and method of thermal drop detection for use in inkjet printing devices.
Inkjet printing devices use ink to print text, graphics, images, etc. onto print media. Inkjet printers may use print cartridges, also known as "pens", which shoot drops of printing composition, referred to generally herein as "ink", onto a print medium such as paper or transparencies. Each pen has a printhead that includes a plurality of nozzles. Each nozzle has an orifice through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page by, for example, a carriage, while shooting drops of ink in a desired pattern as the printhead moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as thermal printhead technology.
In a current thermal system, a barrier layer containing ink channels and vaporization chambers is located between an orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heating elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, the ink in the vaporization chamber turns into a gaseous state and forces or ejects an ink drop from a orifice associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern onto the print media to form a desired image (e.g., picture, chart or text).
Optical drop detect circuits are utilized in inkjet printing devices for a variety of purposes such as verifying the operation of printhead nozzles of an inkjet printhead, determining the relative positions of nozzle arrays of multiple inkjet printheads, and ascertaining the size and location of individual ink drops. Optical drop detect circuits typically include a light sensor, such as a photodiode, which senses the light provided by a light source, such as a light emitting diode (LED). When a drop is present in the light path between the light sensor and the light source, the output of the light sensor changes because the amount of light sensed by the light sensor is reduced by the presence of the ink drop. The output of the light sensor is typically amplified and analyzed to determine whether an ink drop passed through the light path between the light source and the light sensor.
As the pens eject droplets of ink through the printhead nozzle orifices, a certain amount of ink is dispersed within the printing device as aerosol. Print media dust can also be produced within the printing device as the printing device handles print media. This aerosol and dust is contaminant matter that is deposited on the interior surfaces of the printing device, on the pen printheads, and also onto the light source and light sensor of an optical drop detector. The build-up of these contaminants on an optical drop detector reduces the amount of light from the light source that reaches the light sensor. This build-up eventually will cause the optical drop detector to cease to properly operate which can lead to a loss of optical drop detector information. Loss of this information can in turn degrade inkjet printing device output print quality, cause one or more printhead nozzles to fail due to undetected clogging caused by such contaminant matter or dried ink, and shorten the useful life of an inkjet printing device.
Alleviation of these problems would be a desired improvement, thereby maintaining inkjet printing device output print quality, helping prevent printhead nozzle failure, and increasing the useful life of an inkjet printing device. Accordingly, the present invention is directed to solving printing device problems caused by contaminant matter accumulating on printing device optical drop detectors. The present invention accomplishes this objective by providing a thermal drop detector and method of thermal drop detection for use in inkjet printing devices.
An embodiment of the present invention is a thermal drop detector that comprises an array configured to define a plurality of cells each of which is configured to detect thermal changes in an area of that cell resulting from deposition of a drop adjacent that cell. The thermal drop detector additionally comprises a thermally conductive layer over each of the cells to protect each of the cells from physical contact with the drop.
The above-described embodiment of the present invention may be modified and include the following characteristics described below. The array may be configured to define a two-dimensional sheet. Each of the cells may have substantially uniform dimensions.
Each of the cells may be substantially rectangular. In such cases, each of the cells may have an area substantially equal to twenty-five (25) square microns.
The thermally conductive layer may be a one-piece structure. Each cell may include an electrical element. The thermal drop detector may be used in a printing device.
An alternative embodiment of a thermal drop detector in accordance with the present invention comprises a substrate including a plurality of thermally sensitive areas each of which includes an electrical element configured to detect thermal changes resulting from deposition of a drop adjacent that area. The thermal drop detector additionally comprises a thermally conductive layer over each of the areas to protect each of the areas from physical contact with the drop.
The above-described embodiment of a thermal drop detector of the present invention may be modified and include the following characteristics described below. The electrical element may include a diode or a thermistor.
The substrate may include a thermistor. Each of the areas may have substantially uniform dimensions.
Each of the areas may be substantially rectangular. In such cases, each of the cells may have an area substantially equal to twenty-five (25) square microns.
The thermally conductive layer may be a one-piece structure. The thermal drop detector may be used in a printing device.
Yet another alternative embodiment of a thermal drop detector in accordance with the present invention comprises structure for measuring a thermal change resulting from deposition of a drop on a thermally conductive material and structure for determining a characteristic of the drop deposited on the thermally conductive material based upon a thermal change recorded by the structure for measuring.
The above-described embodiment of a thermal drop detector of the present invention may be modified and include the characteristics as described herein. Additionally, the thermal drop detector may be used in a printing device.
An embodiment of a method of thermal drop detection in accordance with the present invention comprises depositing a drop on a thermally conductive material, the thermally conductive material overlaying a thermally sensitive array. The method additionally comprises measuring via the thermally sensitive array a thermal change resulting from deposition of the drop on the thermally conductive material. The method further comprises determining a characteristic of the drop deposited on the thermally conductive material based upon the thermal change measured by the thermally sensitive array.
The above-described embodiment of a method of thermal drop detection in accordance with the present invention may be modified and include the following characteristics described below. The method may further comprise cleaning the thermally conductive material to remove the deposited drop therefrom. The method may further comprise protecting the thermally sensitive array from physical contact with the deposited drop via the thermally conductive material.
Determining a characteristic of the drop deposited on the thermally conductive material based upon the thermal change measured by the thermally sensitive array may include determining a size of the drop, determining a volume of the drop, or determining a location of the drop. The method of may be used in a printing device.
Measuring via the thermally sensitive array a thermal change resulting from deposition of the drop on the thermally conductive material may include generating an electrical signal via an electrical element of the thermally sensitive array that is related to the thermal change.
Other objects, advantages, and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.